This invention relates to corrosion of metals. More in particular the invention concerns the reduction of corrosion of metal members in systems containing both metallic and nonmetallic components.
Most metals, and especially those containing major amounts of iron, are known to corrode, or rust, when exposed to salt water or other environments capable of conducting an electric current and an electric potential. To retard corrosion of metals, various coatings and anodic or cathodic protection techniques have been developed. Such techniques are exemplified in U.S. Pat. Nos. 3,313,721 and 3,477,930; Morgan, Cathodic Protection 253-265 (1959); and Fontana et al., Corrosion Engineering 205-214 (1967).
In certain equipment an electrically conductive liquid solution, i.e. an electrolyte, flows from electrically charged members through nonmetallic conduits and directly into, and through, metallic conduits attached to the nonmetallic conduit. The electrolyte can flow from the metallic conduit to a suitable receiving container for storage or disposal. Oftentimes stray electric current will flow through the electrolyte and cause the metallic conduit to corrode even though this conduit is not in physical contact with the electrically charged member. Corrosion of the metal portion of this system has previously been reduced by inserting a graphite electrode through the nonmetallic conduit, and into the electrolyte, and connecting this electrode to a ground. A portion of the stray current flowing through the electrolyte was removed, and corrosion of the metallic conduit reduced, by means of such an electrode, but corrosion resulting from stray electric current in such an electrode protected system is still excessive.
An apparatus and method is desired to minimize corrosion of metallic conduits in a system including a source of stray electric current, a nonmetallic conduit and an electrolyte.